KVM: Don't pre-reserve xarray entries when storing empty/NULL attributesgrafted

Skip the xarray reservation loop when clearing all memory attributes, as
storing NULL only erases the entry and never needs to allocate, so no
reservation (and no cleanup of a failed one) is required in that case.

Suggested-by: Sean Christopherson <seanjc@google.com>
Cc: David Ballesteros <davimaba.v@proton.me>
Signed-off-by: Zeng Chi <zengchi@kylinos.cn>
Link: https://patch.msgid.link/20260921102442.1232375-1-zeng_chi911@163.com
[sean: split to separate patch]
Signed-off-by: Sean Christopherson <seanjc@google.com>

1 files changed, 73 insertions, 0 deletions

diff --git a/arch/x86/Makefile.um b/arch/x86/Makefile.um
new file mode 100644
index 000000000..9adecd656
--- /dev/null
+++ b/arch/x86/Makefile.um
@@ -0,0 +1,73 @@
+# SPDX-License-Identifier: GPL-2.0
+core-y += arch/x86/crypto/
+
+#
+# Disable SSE and other FP/SIMD instructions to match normal x86
+# This is required to work around issues in older LLVM versions, but breaks
+# GCC versions < 11. See:
+# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99652
+#
+ifeq ($(call gcc-min-version, 110000)$(CONFIG_CC_IS_CLANG),y)
+KBUILD_CFLAGS +=  -mno-sse -mno-mmx -mno-sse2 -mno-3dnow -mno-avx
+KBUILD_RUSTFLAGS += -Ctarget-feature=-sse,-sse2,-sse3,-ssse3,-sse4.1,-sse4.2,-avx,-avx2
+endif
+
+KBUILD_RUSTFLAGS += --target=$(objtree)/scripts/target.json
+
+# The target.json file is not available when invoking rustc-option, so use the
+# built-in target when checking whether flags are supported instead.
+ifeq ($(CONFIG_X86_32),y)
+KBUILD_RUSTFLAGS_OPTION_CHKS += --target=i686-unknown-linux-gnu
+else
+KBUILD_RUSTFLAGS_OPTION_CHKS += --target=x86_64-unknown-linux-gnu
+endif
+
+ifeq ($(CONFIG_X86_32),y)
+START := 0x8048000
+
+KBUILD_LDFLAGS		+= -m elf_i386
+ELF_ARCH		:= i386
+ELF_FORMAT 		:= elf32-i386
+CHECKFLAGS	+= -D__i386__
+
+KBUILD_CFLAGS		+= $(call cc-option,-m32)
+KBUILD_AFLAGS		+= $(call cc-option,-m32)
+LINK-y			+= $(call cc-option,-m32)
+
+LDS_EXTRA		:= -Ui386
+export LDS_EXTRA
+
+# First of all, tune CFLAGS for the specific CPU. This actually sets cflags-y.
+include $(srctree)/arch/x86/Makefile_32.cpu
+
+# prevent gcc from keeping the stack 16 byte aligned. Taken from i386.
+cflags-y += $(call cc-option,-mpreferred-stack-boundary=2)
+
+# Prevent sprintf in nfsd from being converted to strcpy and resulting in
+# an unresolved reference.
+cflags-y += -ffreestanding
+
+KBUILD_CFLAGS += $(cflags-y)
+
+else
+
+START := 0x60000000
+
+KBUILD_CFLAGS += -fno-builtin -m64 
+
+CHECKFLAGS  += -m64 -D__x86_64__
+KBUILD_AFLAGS += -m64
+KBUILD_LDFLAGS += -m elf_x86_64
+KBUILD_CPPFLAGS += -m64
+
+ELF_ARCH := i386:x86-64
+ELF_FORMAT := elf64-x86-64
+
+# Not on all 64-bit distros /lib is a symlink to /lib64. PLD is an example.
+
+LINK-$(CONFIG_LD_SCRIPT_DYN_RPATH) += -Wl,-rpath,/lib64
+LINK-y += -m64
+
+vdso-install-y += arch/x86/um/vdso/vdso.so.dbg
+
+endif